EFFECTS OF DIETARY CRUDE PROTEIN, BREED, PARITY, AND HEALTH-STATUS ONTHE FERTILITY OF DAIRY-COWS

A study was conducted to determine the impact of dietary CP (13% vs. 2 0%), parity (first vs. second lactation or later), and breed (Holstein vs. Jersey) on the reproductive efficiency of dairy cows. Sixty-four cows were blocked by parity and breed and assigned to one of two treat ments. Cows were removed from treatments on d 100 or 120 depending on pregnancy status. Cows were categorized by health status based on the occurrence of postparturient disorders. Plasma urea N concentrations w ere influenced by diet (8.6 vs. 21 mg/dl, 13 and 20% CP, respectively) , parity, and breed. Reproductive indices were not influenced by diet except that days to first estimated ovulation increased for cows fed t he 20% CP diet when health status was added to the model. Days to firs t observed estrus, first AI service, and cumulative pregnancy rate wer e affected by health status. Regression analysis for survival showed a n interaction of diet and health status for days open. High CP diets t ended to increase days open when cows had major health problems; other wise, a high CP diet decreased days open. The implementation of a stri ct reproductive management program allowed high reproductive efficienc y goals to be achieved regardless of plasma urea N concentrations.